Corrected entry: The computer that the T-1000 reads in the police car at the beginning states that John is 10 years old and was born in February of 1985. Also Sarah Conner is said to be 29 in this film, she was about 19 when she had John, also reinforcing the fact that John is supposed to be 10 years old. It is obvious both by the appearance of the actor and the behaviour of the character that he would be about 14 or 15 years old rather than the prescribed 10.
Jazetopher
14th Aug 2006
Correction: How is it obvious? He might very well "look" older, but his mother was arrested for blowing up a building, and sent to an institution for her story about the future. He has gone from his mom dating all these guys and training him for the future war, which she told him all about, to living with a foster family. His behavior is likely the result of the fact that he was pyscologically damaged, and that nobody ever really gave a care about him after his mom was taken away, as he is rebelling.
Jazetopher